1. Field of the Invention
The present invention relates to a three-dimensional reference image segmenting method and device and an object discrimination system, and more specifically to a three-dimensional reference image segmenting method and device for extracting only a previously stored three-dimensional reference image from an input three-dimensional image, and and an object discrimination system utilizing the same method.
2. Description of Related Art
In the prior art, there has been known an image processing method for picking up or extracting a reference image included in an input image ("segmentation"). In this specification, the verb "segment" is often used as the verb meaning the "segmentation".
Briefly, an input image is divided into small image domains permitted to be overlapped to each other, and is Fourier-transformed for each small image domain. Further, each small image domain is transformed into the pattern of a Fourier power spectrum, and a template matching processing (segmentation) is conducted between the pattern of the Fourier power spectrum and a previously prepared reference image (standard pattern) By using as a mask a "candidate" pattern thus extracted or segmented, the pattern of the Fourier transformation is filtered, and then, a inverse Fourier transformation is conducted. Thus, a pattern matching resistive to noise is conducted by using the pattern obtained by the inverse Fourier transformation. One example of this method is disclosed in Japanese Patent Application Laid-open Publication No. JP-A-02-156387.
However, the above mentioned prior art method can process only a two-dimensional image. In other words. the above mentioned prior at method cannot be applied to the case of segmenting a previously stored three-dimensional reference image from a three-dimensional input image. Under this circumstance, in the prior art, there is proposed a method for extracting or segmenting, a three-dimensional reference image from a input image, by extending the above mentioned prior art method to input images which correspond to images obtained by viewing an object by a left eye and a right eye, respectively. In brief each of the input images is divided into small image domains permitted to be overlapped to each other, and is Fourier-transformed for each small image domain. Parallax between a left eye image and a right eye image is expressed as a phase difference in a Fourier transformation. This method is disclosed in Japanese Patent Application Laid-open Publication No. JP-A-07-287762.
According to this second prior art method, it is possible to precisely extract or segment only a target image from even an image including not only a reference image but also an image other than the reference image, by calculating the phase difference in a Fourier transformation of left and right eye images, for input images corresponding to the left eye image and the right eye image and a reference image, and predicting, from the input images, an image which is consistent with the reference image, in factors including the parallax.
In Japanese Patent Application No. Heisei 06-184785 filed on Aug. 5, 1994 and laid open as Japanese Patent Application Laid-open Publication No. JP-A-08-050654 on Feb. 20, 1996, the inventor of this application has proposed a three-dimensional reference image segmenting method and device, capable of precisely segmenting only a reference image even if a reference image and a three-dimensional image to be extracted included in an input image are difference in a position of a depth direction. In brief, a parallax between a left eye image and a right eye image in the reference image is expressed as a power spectrum pattern, and on the other hand, a power spectrum pattern of the three-dimensional image to be extracted is obtained from a spatial frequency filtering which uses only a maximum power spectrum of the reference image and the input image, and therefore which does not include information concerning the phase difference between the left eye image and the right eye image.
In the above mentioned three-dimensional reference image segmenting method and device, the parallax between the left eye image and the right eye image is expressed by obtaining a sum of vectors, on a complex plane, of local Fourier transformed images for the left eye image and the right eye image, and then, a pattern in change of the vector sum corresponding to the change of the phase difference, or expressed as the power spectrum pattern corresponding to the change of the phase difference. Thereafter, the image having the power spectrum pattern similar to that of the reference image is predicted within the input image, so that segmentation of the three-dimensional reference image is conducted. Accordingly, even if the same image as the reference image is included in the input image, if the reference image and the image to be extracted included in the input image are different in the power spectrum pattern, a precise segmentation cannot be executed. This is disadvantageous.
Here, the difference in the power spectrum pattern between the reference image and the image to be extracted included in the input image, is attributable to the followings Assume that, in a stereogram as shown in FIGS. 3A and 3B, a left eye image as shown in FIG. 3A and a right eye image as shown in FIG. 3B are used as the reference image, and on the other hand, the input image is constituted of an image including a doll image corresponding to the situation in which a doll whose image is shown in FIGS. 3A and 3B is rotated around an axis extending from a top of a head of the doll toward to legs of doll. In this situation, a point before a converging point and another point behind the converging point are different in the parallax between the left eve image and the right eye image. This difference causes the difference in the power spectrum pattern between the reference image and the image to be extracted included in the input image.
In other words, the case that the power spectrum pattern is different between the reference image and the image to be extracted included in the input image, corresponds to the case that the image to be extracted included in the input image involves a rotation which causes to change the depth direction, and therefore, between the reference image and the image to be segmented, a sighting view is different because of difference in depth. In this situation, the above mentioned three-dimensional reference image segmenting method and device cannot execute a precise segmentation of the target image.
One means for overcoming the problem in the case that the power spectrum pattern is different between the reference image and the image to be extracted included in the input image, is disclosed by Martin Lades, Jan C. Vorbruggen, Joachim Buhmann, Jorg Lange, Christoph v.d. Malsburg, Rolf P. Wurtz, and Wolfgang Konen. "Distortion Invariant Object discrimination in the Dynarnic Link Architecture", IEEE Transactions on Computers, Vol. 42, No. 3, pp.300-311 (March 1993), the disclosure of which is incorporated by reference in its entirety into this application.
This approach is featured in that a difference between a reference image and an input image is investigated for each local image domain by using a two-dimensional projected image of a three-dimensional image. However, this approach is disadvantageous in that (1) the three-dimensional image cannot be directly handled, and the two-dimensional projected image is necessary; (2) the image of each local image domain is displayed in a bit map format, and the amount of change which gives the maximum degree of matching is investigated while shifting the image in an X direction and in a Y direction. Therefore, the processing needs a vary long time, and cannot practically be applied to a large scale image; and (3) image deformation in each local image domain lowers the capability of discrimination between different objects.